The present invention relates to a fuel supply system for an internal combustion engine which may supply always the fuel in such a ratio that the pollutant content in the engine exhaust may be minimized under any operating conditions of said engine.
The content of the pollutants in the engine exhaust is dependent upon the air-fuel ratio of the air-fuel mixture to be burnt, and the emission of pollutants may be minimized when the air-fuel ratio is maintained within a certain range slightly leaner than the stoichiometric air-fuel ratio. The conventional engines with a carburetor are in general so designed that the air-fuel mixture with an air-fuel ratio slightly leaner than the stoichiometric ratio may be charged into the engine under the medium load under which the engine is most frequently driven. Therefore the emission of pollutants under the medium load may be minimized, but the suction of gasoline increases under the light and heavy load in excess of the intake air quantity because of the inherent construction of the conventional carburetors, thus resulting in the excessively rich air-fuel mixture. As a result the pollutant content in the engine exhaust is increased. In case of the automotive internal combustion engines, they are generally driven under the medium load about 80% of the traveling milage, but the frequency of driving under the light or heavy load is extremely increased in the urban area. Therefore one of the air pollution problems in the automotive industry is to reduce the automotive pollutants even under the light or high load condition.